There has been a recent and evolving media blitz concerning the potential use of medical marijuana (tetrahydrocannabinol, THC) in Parkinson’s disease patients. All of the attention to marijuana has been largely a result of multiple states passing legislation to legalize and to regulate the drug; or to alternatively make it available for select medical diagnoses. In this month’s National Parkinson Foundation What’s Hot in Parkinson’s Disease column, I will review the current state of the research into medical marijuana for Parkinson’s disease.

A recent report from the guideline development subcommittee of the American Academy of Neurology (AAN) tackled the evidence-base supporting the use of marijuana for neurological disorders. Spasticity, central pain syndromes and bladder dysfunction (disorders not including Parkinson’s disease) seemed to be improved with marijuana use. The few available studies revealed that marijuana was not helpful in Parkinson’s disease related tremor or levodopa-induced dyskinesias. The report was careful to outline the risks and the benefits of medical marijuana, and it recommended education and counseling for anyone considering this option. The risk of serious psychopathologic effects (hallucinations, etc.) was cited to be about 1%.

In addition to the AAN report, there have been a few recent papers supporting the use of marijuana for specific Parkinson’s disease symptoms (motor, mood, quality of life, sleep), however all have suffered from methodological issues such as including small numbers of patients, and not including a proper control group. Katerina Venderova in 2004 (Movement Disorders Journal) conducted a survey of Parkinson’s disease patients on marijuana (cannabis) and reported that “39 patients (45.9%) described mild or substantial alleviation of their PD symptoms in general, 26 (30.6%) showed improvement of rest tremor, 38 (44.7%) had improvement in bradykinesia, 32 (37.7%) had alleviation of muscle rigidity, and 12 (14.1%) had improvement of L-dopa-induced dyskinesias. Only 4 patients in this survey (4.7%) reported that cannabis actually worsened their symptoms. Patients using cannabis for at least 3 months reported significantly more alleviation of their Parkinson’s disease symptoms in general.” Like Venderova who conducted her survey in Prague, we have also had Parkinson’s disease patients phone us at the free 18004PDINFO National Parkinson Foundation hotline, and detail personal experiences and positive stories supportive of marijuana in Parkinson’s disease. Collectively, the problem with all of these types of personal reports has been the lack of scientific rigor necessary to truly understand the effects of marijuana on Parkinson’s disease.

In a recent review in the New England Journal of Medicine, the National Institute on Drug Abuse (NIDA) Director Dr. Nora Volkow carefully outlined the adverse health effects of marijuana use. In her article Dr. Volkow pointed out that marijuana, which is thought of by much of the public as a completely harmless drug, can have serious adverse effects. She makes the following important points:

In the U.S. it is the most commonly used “illicit” drug

12% of those 12 years or older used it in the past year

Smoking is the most common way people use marijuana and this can harm the lungs

There are available edible forms including teas and foods

Approximately 9% of users will become addicted, and there may be a withdrawal syndrome which can make quitting difficult for some users

Use in adolescence and early adulthood can contribute to worsening brain function, decreased connections between brain regions, and a decrease in IQ

Heavy marijuana use can rarely lead to psychosis and hallucinations

Marijuana can reduce cognitive and also worsen motor function

Your risk of a car accident doubles if you have recently smoked marijuana

The potency of the THC content in marijuana has increased from 3% to 12% in the last several decades making accidental overdoses, especially with food products, much more common

The best evidence supporting marijuana use has been shown in glaucoma, nausea, the AIDS wasting syndrome, chronic pain, multiple sclerosis, and epilepsy

Scientifically it is not crazy to think that marijuana may play some positive role in the alleviation of Parkinson’s disease symptoms. There are cannabinoid (THC) receptors all over the brain, and these receptors seem to be concentrated in a region important to Parkinson’s disease, commonly referred to as the basal ganglia. In fact, the globus pallidus and the substantia nigra pars reticulata, which are structures within the basal ganglia, are some of the most densely packed cannabinoid (THC) receptor areas in the human body. It is therefore not beyond reason to think that a drug directed at these receptors might positively influence the symptoms of Parkinson’s disease. Indeed, many drug companies remain interested in compounds influencing these receptors.

What is the bottom line for information that a person with Parkinson’s disease will need to know if considering medical marijuana. Marijuana should never be thought of as a replacement for dopaminergic and other approved therapies for Parkinson’s disease. Second, though most available large studies have not shown a benefit, that does not mean that there will not be a benefit. Much more research will be needed to understand which patients, which symptoms, and how best to safely administer medical marijuana in Parkinson’s disease, especially over the long-term. It may turn out that non-motor features such as depression, anxiety, and pain respond best, but studies are desperately needed to sort this out. Parkinson’s disease patients living in states where marijuana has been legalized for medical use should be aware of the dangers outlined by Dr. Volkow, particularly the effects on the lungs, the dangers of driving, and accidental overdoses (particularly with food items). Finally, states will need to develop training programs for doctors and medical teams prescribing marijuana, so that the Parkinson’s disease patient on medical marijuana can be kept as safe as possible.